1. Field of the Invention
The invention relates to novel sizing compositions, their preparation and use.
2. Description of the Related Art
The use of curing components in sizes based on blocked polyisocyanates is known, for example, from EP-A 0 792 900. Aralkylamine-blocked polyisocyanates and their particular suitability in sizes, especially glass fibre sizes, is not described.
The major compounds used for the blocking of polyisocyanates are ε-caprolactam, butanone oxime, malonates, secondary amines, and triazole and pyrazole derivatives, as described, for example, in patents EP-A 0 576 952, EP-A 0 566 953, EP-A 0 159 117, U.S. Pat. No. 4,482,721, WO 97/12924 or EP-A 0 744 423.
Secondary amine blocking agents, including aralkyl-substituted amines, are known from EP-A 0 096 210. The use of such amines in aqueous systems, particularly in sizes, however, is not known from EP-A 0 096 210.
Although the formula depicted on page 2, lines 20–24 of EP-A 0 096 210 embraces a large number of diamines, page 3 line 8 ff. nevertheless points out that all secondary amines are suitable blocking agents. According to page 5 lines 20–29, only a very small number of such diamines is listed as being suitable. The examples on page 9 and 10 as well relate only to dialkylamines such as diisopropylamine, substituted secondary cycloaliphatic amines such as substituted cyclohexylamines or cycloaliphatic N-heterocycles such as 2,2,4,6 tetramethylpiperidine. With the exception of diisopropylamine, these compounds are reacted with isocyanates at temperatures of at least 120° C., and so the person skilled in the art must assume that the elimination of these blocking agents, necessary for further reaction, takes place only at much higher temperatures.
EP-A 0 178 398 specified solid blocked isophorone diisocyanate as a curing agent for powder coating materials. Here again, aralkyl-substituted secondary amines as blocking agents and N-tert-butyl-benzylamine were mentioned, albeit without a specific example. EP-A 0 787 754 claimed such blocking agents for selected polyisocyanates as curing agents for powder coating materials; N-tert-butyl-benzylamine or other aralkyl-substituted diamines, however, are mentioned neither in the disclosure nor in the examples. Liquid solvent-based formulations or aqueous or water-dilutable blocked polyisocyanates, and especially their suitability for sizes, are mentioned in neither document.
In preparing sizes, especially glass fibre sizes, water-dispersible or water-soluble isocyanates are used, usually blocked with ε-caprolactam and butanone oxime.
Whereas in the case of ε-caprolactam-blocked isocyanates it is common to employ baking temperatures around 160° C., blocked curing agents for which butanone oxime was the blocking agent used can be deblocked at temperatures 10–20° C. lower. At these temperatures, however, in many sizes the desired properties are no longer achieved. Moreover, high deblocking and/or drying temperatures often result in an unwanted thermal yellowing of the sizes. Furthermore, these deblocking temperatures are now perceived as being too high, on cost grounds, so giving rise to a demand for sizes comprising crosslinker systems which crosslink at lower temperatures than in the case of butanone oxime.
The principle of the preparation of water-dispersible or water-soluble blocked polyisocyanates is known and is described, for example, in DE-A 24 56 469 and DE-A 28 53 937.